The present invention relates generally to the field of commercial FM broadcasts, and specifically to a digital format broadcast system for U.S. commercial FM broadcasts.
FM radio broadcastsxe2x80x94regulated in the United States by the Federal Communications Commission (FCC)xe2x80x94are allocated to 100 carrier channels (channels 201-300), assigned to the frequency range 88 MHz to 108 MHz, with each carrier channel comprising 200 KHz of bandwidth. Channels 201-220, with carrier frequencies at 88.1 MHz to 91.9 MHz, are reserved for non-commercial educational broadcasts. The remainder of the FM channels, from 92.1 MHz to 107.9 MHz, are allocated to commercial FM broadcasts. As used herein, however, the term xe2x80x9ccommercial FM broadcastsxe2x80x9d refers to all FCC-regulated broadcasts in the frequency range 88 MHz to 108 MHz. The vast majority of commercial FM stations broadcast in an analog stereo audio format, and are thus restricted to a single stream of audio (e.g., voice or music).
Recent developments in digital wireless communications services have proven that the wireless communication of information in a digital format makes dramatically more efficient use of the wireless spectrum than does transmission of the same information in an analog format. Various digital FM broadcast formats and transmission models have been proposed. For example, one system contemplates the simultaneous broadcast of standard FM analog audio within the existing 200 KHz bandwidth channels, with the additional broadcast of digital format content at a lower power in the frequencies immediately adjacent the FM channel. While this proposal maintains the functionality of existing analog commercial FM receivers, it requires extensive modification to commercial FM transmission stations to broadcast the digital information in new frequencies, as well as requiring licensing of additional spectrum.
The present invention relates in one aspect to a method of broadcasting services in a digital format comprising at least one digital bitstream. The method includes time-division multiplexing the bitstream(s) into one or more time slots comprising a data frame, and frequency modulating the resulting data frames around a single carrier frequency into a commercial FM broadcast signal. The signal is transmitted on a commercial FM broadcast station such that substantially the entire spectrum of the transmission comprises the digital data frames. The broadcast services may comprise FM audio programs; foreign language audio programs; paging messages; information services such as news, stock information, sports information, and weather information; entertainment services such as movies, audio programs, and games; and computer programs. In one embodiment, the bit rate(s) of the digital bitstream(s) is monitored, and the bitstream(s) may be reallocated to time slots in the data frames based on changes in the bit rate(s).
In some embodiments, the time-division multiplexing may comprise a TDMA wireless communications protocol, such as GSM, IS-54, USDC, PDC, MIRS, PACS-UB, DCS 1800, or PHS. In some embodiments, the frequency modulation may comprise a wireless communications protocol, such as GMSK, 8-PSK, xcfx80/4 DQPSK, xcfx80/4 DQPSK, 16-QAM, or GFSK.
In another aspect, the present invention relates to a system for broadcasting services in a digital format. The system includes a source of services formatted into at least one digital bitstream, a multiplexer for time-division multiplexing the digital bitstream(s) into one or more time slots comprising a data frame, a modulator for frequency modulating the data frames around a single carrier frequency into a commercial FM broadcast signal, and a transmitter for transmitting the broadcast signal on a commercial FM broadcast station such that substantially the entire spectrum of the transmission comprises the digital data frames. In one embodiment, the system additionally includes a controller operative to periodically monitor the bit rate(s) of the digital bitstream(s), and to reallocate the digital bitstream(s) to time slots in response to changes in the bit rate(s).
In another aspect, the present invention relates to a method of upgrading an analog format commercial FM broadcast station to digital format. The method includes providing the analog format content in at least one digital format bitstream. The existing signal modulator is replaced with a modulator operative to time division multiplex the at least one digital bitstream into a series of data frames. The data frames are then frequency modulated around a single carrier frequency and broadcast in conformance with commercial FM broadcast standards.
In another aspect, the present invention relates to a method of upgrading an analog format commercial FM broadcast station to simultaneously transmit both analog and digital format signals. A digital modulator and transmitter are provided, where the digital transmission is separated from the analog transmission by at least 9.8 MHz. The analog and digital transmission signals are then diplexed onto an existing broadcast tower antenna.
In yet another aspect, the present invention relates to a method of simultaneously broadcasting a signal in analog and digital formats. An analog format signal is broadcast on a first commercial FM broadcast station, frequency modulated around a first carrier frequency. The analog format signal is digitized into at least one digital bitstream, frequency modulated around a second carrier frequency, and broadcast on a second commercial FM broadcast station non-adjacent to the first commercial FM broadcast station, and in one embodiment, separated from the first station by at least 9.8 MHz.
In another aspect, the present invention relates to a digital FM receiver that is operative to receive multiple content streams, and distribute them to different users, such as via a wired or wireless network transmission medium.
In still another aspect, the present invention relates to a digital FM receiver that is operative to receive at least one content stream, and utilize empty or non-received channels in the digital data frame to reduce power or to search the FM band for other digital broadcasts.